1. Field of the Invention
The present invention relates to a thermal transfer image-receiving sheet and a surface condition improver, and precisely to a thermal transfer image-receiving sheet having high sensitivity and having few image defects and to a surface condition improver to be used in producing it.
2. Background Art
Heretofore, various thermal transfer recording methods are known; and above all, a dye diffusion transfer recording system is specifically noted as a process capable of producing color hard copies of which the image quality is the nearest to that of the images of silver salt photographs (for example, see “New Development of Information Recording (hard copy) and its Material”, issued by Toray Research Center, 1993, pp. 241-285; and “Development of Printer Material”, issued by CMC, 1995, p. 180). Moreover, as compared with silver salt photography, the system has various advantages in that it is a dry system, it enables direct visual image formation from digital data, it facilitates image duplication.
In the dye diffusion transfer recording system, a dye-containing thermal transfer sheet (hereinafter this may be referred to as “ink sheet”) and a thermal transfer image-receiving sheet (hereinafter this may be referred to as “Image-receiving sheet”) are put one upon another, then the ink sheet is heated with a thermal head from which the heat generation is controlled by an electric signal applied thereto, to thereby transfer the dye from the ink sheet to the image-receiving sheet for image information recording thereon. In the system, three colors of cyan, magenta and yellow may be transferred and recorded as overlaid, thereby giving a color image having a continuous color density gradation.
In the image-receiving sheet of this system, a receiving layer on which the transferred dye is fixed is formed on the support thereof, and in general, for increasing the adhesiveness between the image-receiving sheet and the transfer sheet, for example, a highly-cushionable layer such as a foam layer comprising a resin and a foaming agent or a porous layer containing a hollow polymer is formed between the support and the receiving layer (for example, see JP-A11-321128 and JP-A 2006-88691).
JP-A 11-321128 discloses a technique of forming, on a support, an interlayer comprising mainly hollow particles and an organic solvent-resistant polymer by coating and drying thereon, and then forming a receiving layer out of an organic solvent-based resin coating liquid applied thereto. In this, the organic solvent-resistant polymer for the interlayer plays a role of preventing the hollow particles in the interlayer from dissolving in the organic solvent in the receiving layer. However, the method of forming the receiving layer out of an organic solvent-based resin coating liquid has some problems in that the sensitivity is insufficient and the cost is high, and therefore, it is desired to improve the method in point of overcoming image defects (e.g., white spots) and increasing the transfer density.
On the other hand, a thermal transfer image-receiving sheet fabricated by water-base simultaneous multilayer coating is known (JP-A 2006-88691). This discloses a technique of simultaneous multilayer coating with a latex-containing coating liquid and a hollow particle-containing coating liquid thereby producing a thermal transfer sheet having high-density printing characteristics and excellent in printing uniformity. However, this has no description relating to incorporating a compound in the layer of the image-receiving sheet to thereby improve the properties of the sheet.
In addition, the simultaneous multilayer coating requires simultaneous coating with coating liquids containing a bulky solid substance in a high concentration, different from coating for conventional silver halide photographic materials, and therefore, it is technically difficult to attain coating surface uniformity of the thermal transfer image-receiving sheet obtained by simultaneous multilayer coating, and further improvements are desired.
On the other hand, JP-A 8-146556 and JP-A 10-234995 describe adding the compound for use in the invention to a support or inkjet image-receiving sheet as a preservative; but they are silent on adding it to the coating layer of a thermal transfer image-receiving sheet. In addition, JP-A 8-146556 and JP-A 10-234995 are silent on problems in surface modification and on a method for solving them.